This application proposes a 4-year plan to provide the candidate with mentored research and career development training. The candidate has recently completed a 3-year K12 award (Pediatric Scientist Development Program), and desires additional mentored support to facilitate her scientific and career goals. The ultimate goal of the candidate is to be an independent investigator at an academic medical center, studying factors that regulate normal and malignant hematopoiesis. The experiments outlined in this application aim to understand the role of the transcription factor Kruppel like factor 7 (KLF7) in T cell development. The proposed studies will be carried out at Washington University under the primary mentorship of Dr. Daniel Link, a leader in the field of hematopoiesis and a highly experienced and regarded mentor. As the proposed studies are a new avenue of study for the candidate, Dr. Takeshi Egawa, an expert in thymocyte development, will serve as a co-mentor and provide technical guidance on the study of T cells. Expression of KLF7 is increased in therapy-resistant pediatric ALL and is an independent predictor of relapsed disease (Flotho, et al; Blood 2007). The KLF family of transcription factors is involved in numerous aspects of blood cell development; however a role for KLF7 in hematopoiesis has not been previously described. Since KLF7 target genes include several implicated in hematopoietic stem and progenitor (HSPC) maintenance, we hypothesized that KLF7 may play a role in regulating normal HSPC function, and may contribute to leukemogenesis or therapy resistance. We show in preliminary data that enforced expression of KLF7, while markedly inhibiting HSC repopulating and self-renewal capacities, results in the relative preservation of T cells, increased expression of the anti-apoptotic factor BCL2A1, and reduced apoptosis of CD4- CD8-(DN) thymocytes. KLF7 is expressed throughout T cell development, peaking at the CD4+ CD8+ (DP) stage of thymocyte development. Loss of KLF7 is associated with decreased numbers of early thymocytes. Based on our preliminary data and the prominent role of the KLF family in regulating T cells, we hypothesize that KLF7 regulates thymocyte development and commitment to the T cell lineage. Furthermore, overexpression of KLF7 suppresses apoptosis of early thymocytes and may contribute to chemotherapy resistance in ALL. The specific aims proposed are: 1) Determine whether KLF7 directs the commitment of multipotent progenitor cells to a T cell fate; and 2) Determine the contribution of KLF7 to thymocyte survival, proliferation and maturation. In addition, we propose to identify targets of KLF7 in thymocytes, and to further elucidate the role of BCL2A1 in mediating the survival of DN thymocytes overexpressing KLF7. Future studies will investigate the role of the identified targets in T cell development and in potentially mediating the therapy-resistance of leukemia cells. Ultimately, inhibition of KLF7 or its downstream targets could potentially be used to sensitize chemotherapy- resistant cells, providing a targeted approach to the treatment of refractory or relapsed leukemia.